Nozzle system and fuel oil burner incorporating it



Sept. 27, 1966 McCULLOUGH 3,275,059

NOZZLE SYSTEM AND FUEL OIL BURNER INCORPORATING IT 2 Sheets-Sheet 1Filed May 10, 1965 INVENTOR.

John E. Mc Cullough fin; 4

Attorney Sept. 27, 1966 NOZZLE SYSTEM AND FUEL OIL BURNER INCORPORATINGIT Filed May 10, 1965 J. E. MCCULLOUGH 3,275,059

2 Sheets-Sheet 2 4 (fmmwz INVENTOR.

John E. Mc Ouilough BY United States Patent vO "ice 3,275,059 NOZZLESYSTEM AND FUEL OIL BURNER INCORPORATING IT John E. McCullough,Carlisle, Mass., assignor to Arthur D. Little, Inc., Cambridge, Mass., acorporation of Massachusetts Filed May 10, 1965, Ser. No. 454,393 13Claims. (Cl. 158--28) This invention relates to nozzle systems and moreparticularly to nozzle systems suitable for use with ultra?sonic-atomizers in fuel oil burners or with atomizers which deliver to acombustion zone low-energy spray particles of relatively wide sizedistribution.

Recent developmental work in liquid fuel oil burners has. been directedto the use of ultrasonic atomizers to replace the more conventionalhigh-pressure spray nozzle burners. The ultrasonic atomizers have amongother advantages the ability to operate on very low fuel feed rates,e.g. less than one-half gallon per hour. Thus the use .of ultrasonicatomizers offers the possibility of making low firing rate oil burnersfor such uses as space heaters and home water heaters. Extensiveexperiments with these ultrasonic atomizers has shown, however, that theoil spray produced d-ifiers from that produced by a highpressure spraynozzle in that the droplets lack significant kinetic energy. Instead ofthe droplets leaving the nozzle in a well-defined cone-shaped pattern,they tend to drift off thetransducer horn tip and immediately descendunder the influence of gravity. This action produces an asymmetric mistcloud which must be mixed with highly turbulent air before cleancombustion can be attained in the small volume. Moreover, the ultrasonicatomizers tend to produce droplets having a relatively larger sizedistribution than a high-pressure spray nozzle for example. It wouldtherefore be desirable to have a nozzle system which in its design andoperation would be capable of burning large oil droplets and at the sametime be capable of achieving thorough clean combustion even in a verysmall volume.

In addition to the ultrasonic atomizers used as an example in thedescription of the nozzle system which follows, there are also underconsideration low-pressure spray nozzles which deliver low-energy,relatively large and widely sized liquid oil particles to the combustionzone. The nozzle system of this invention is applicable for use withthis type of nozzle or any nozzle which delivers fuel oil droplets ofthe characteristics noted.

It is therefore a primary object of this invention to provide a nozzlesystem adapted for use with an atomizer which delivers relativelylow-energy fuel oil particles for combustion with a combustion fluid,e.g. air. It is another primary object of this invention to provide anozzle system to augment the performance of the ultrasonic atomizers sothat clean combustion is achieved. It is another object of thisinvention to provide a nozzle system of the character described'whichmakes it possible to achieve efficient and clean burning of fuel oilatomized -by an ultrasonic device even though the power into theultrasonic atomizer is not optimum. An additional object is to provide anozzle system suitable for use with low-pressure spray nozzles. It isanother object of this invention to provide such a nozzle system whichis suitable for use in a burner designed to operate on very low feedrates, e.g., of the order of one-half to one gallon per hour or less. Itis another object of this invention to provide an improved fuel oilburner incorporating an ultrasonic atomizer suitable for suchapplications as space heaters and home Water heaters. Other objects ofthe invention will in part be obvious and will in part be apparenthereinafter.

Patented Sept. 27, 1966 As noted above, the nozzle system is suitablefor use with atomizers delivering relatively low-energy particles forburning. For convenience in describing the nozzle system of thisinvention it Will be discussed and illustrated in detail with referenceto its use use with an ultrasonic atomizer. It is, however, to beunderstood that other atomizers may be used in place of the ultrasonicatomizer shown.

The invention accordingly comprises the features of construction,combination of elements and arrangement of parts which will beexemplified in the construction hereinafter set forth, .and the scope ofthe invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the inventionreference should be had to the following detailed description taken inconnection with the accompanying drawings in which.

FIG. 1 is a longitudinal cross-section of the nozzle system of thisinvention showing its relationship to an ultrasonic atomizer;

FIG. 2 is .a cross-section of the nozzle system of FIG. 1 taken alongline 2r-2 of FIG. '1; and

FIG. 3 is a cross-section of a portion of the forward end of the nozzlesystem showing another corner configuration.

A number of ultrasonic atomizers, along with their attendant fuel supplyand mounting means have been developed; Among these may be cited theatomizer disclosed in U.S.P. 3,162,386 and US. application Serial No.356,323, filed in the name of Robert R. Perron and assigned to the sameassignee as the present invention. Typically these ultrasonic atomizerscomprise a transducer, which includes a stepped horn and anelectromechanical means for driving it, and a power supply means whichincorporate some type of feedback means to insure that the transducer isdriven at its resonant frequency. In addition, means are provided tointroduce the fuel oil which is to be atomized at the atomizing surface,i.e., the small diameter surface of a stepped horn, to clamp thetransducer with an opposing mass stub and to mount the transducer. Theultrasonic atomizer is not a part of the present invention and istherefore illustrated in a typical form in the drawings. It is of courseto be understood that any ultrasonic device capable of atomizing fueloil at an atomizing surface, or other atomizer delivering lowenergyparticles, may be used in conjunction with the nozzle system of thisinvention.

FIG. 1' illustrates the nozzle system of this invention in a fuel oilburner using an ultrasonic atomizer. The

ultrasonic atomizer illustrated in FIG. 1 is that Wlhlch is disclosed inthe above-identified application Serial No. 356,323; The atomizer,generally indicated by the numeral 10, comprises a stepped horn formedof a large diameter section 11 and a small diameter section 12 joinedthrough a fillet. The free surface 13 of the small diameter section 12is the atomizing surface and fuel oil is delivered to it by means of asuit-able fuel line 14. The fuel oil feed line extends internally of thelarge diameter section 11 and runs centrally through the small diametersection 12 opening out into surface 13 as shown by the dot-ted lines.The transducer horn is driven :by a pair of piezoelectric crystals 18and- 19 having an electrode 20 positioned therebetween. Anopposing massstub 21, in the transducer of FIG. 1 having acoustic characteristicssimilar to those of the driving horn, is clamped to the driving horn bymeans of flanges 22 and 23, which are integral parts of the driving hornand the opposed mass stub, and bolts 24. Power to the electrode isbrought in through suitable lead Wires, here illustrated as 25, from apower-feed back circuit shown diagrammatically at 26. Means must beprovided .to mount the entire transducer within the burner and this isdone. through the use of a supporting system comprising three pins 27free to move radially within drilled holes 28 in the'opposed mass stub.The pins in turn are mounted in a support ring 29 which in turn areaffixed to the internal Wall of the forward burner housing 30. I v

The main burner housing is comprised, in addition to the forward housing30 of an after housing section 32. I

joined to the forward section 30 by means of shoulder 33. The forwardhousing 30 which is associated with the nozzle system is closed by thenozzle block as de-. scribed subsequently.

The remaining portion of the burner, other than the. nozzle system whichis to'be described, comprises a light pipe 40 which extends into thehousing and is associated with a photocell 41. This light pipe isdesigned to concentrate radiation from the combustion zone to actuatethe "photocell which in turn is connected through suitable lead wires 42to an electrode control mechanism shown:

diagrammatically at 43. This in turn is connected to an electrode powersupply 44 which supplies, throughlead wires 45, the necessary power tothe electrode 46 which over a portion of its length is suitablyinsulated in a ce-' ramic insulator 47. As will be seen inFIG. 2 asecond electrode 48 contained within an insulator 49 is also provided toform with electrode 46 the required ignition spark. It is preferable toposition these'electrodes so.

that they do not fall in the plane of the atomizing surface 13. When theelectrode tips are positioned slightly behind the atomizing surface 13,fuel oil droplets cannot collect on the electrodes and carbonize thereonto foul them. To complete the burner there are provided means forintroducing air into the housing such as' the blower showndiagrammatically as fan 50. Associated with the housing are also meansfor controlling the amount of air preferably from one piece of metal, itcan be thought to consist of a forward plate 62 which serves as theforward end plate of housing section 30. Within this forward plate 62 isa central opening 63 which communicates with a central channel 64drilled in the nozzle block. An

afterplate 65 having a central opening 66 defines the up- 1 stream endof the nozzle block. The stepped horn of the atomizer is positionedWithin the fuel oil burner so that the small diameter section 12 extendsthrough central opening 66 into the central channel 64 of the nozzleblock. The small diameter section 12 of the-stepped horn-in this portiondefines with the back plate 65 of the nozzle block an annular channelthrough which air is directed as in-,

dicated by the arrows.

The nozzle block can be considered to have a central section designatedby the number 68. .As will be seen in FIG. 2 this central section hasa'series of air passage 69 drilled in it in a manner to provide for thetangential introduction of combustion air into the central channel 64.

deteriorate it without sulfering the reduced light intensity which.would be experienced it the light responsive means a were positioned atthe end of an open sight tube. The combustion cone; 61 is seen to beformed of a comcal section :75 which terminates at the burner end in aflange 76 and in a lip portion 77 at the other end. The

combustion zone established within the combustion cone extends beyondthe cone through a large forward opening 78. The flange 76 of thecombustion cone is mounted to theexternal wall of the end plate 62through an appropriately shaped, heat-resistant; gasket 80. It ispreferable, as illustrated in FIG.. 1, to extend the cone flange;

76 and the gasket 80 to covertheentire front face of the nozzle systemto provide anfefiicient' heatshield or barrier. Thisthermally insulatesvthe nozzle system, .aswell as the remaining portion-of the atomizer,from thefheat of the combustion zone.

FIG. 3 is a cross-section of the forward'end oftheburn er showing a.modification' in the configuration'of the. It will'be seen 'in thismodification combustion cone. that the conical section 75 terminatesin'a roundedishoul der82. FIG. 3 also illustrates theapproximateconfig'uration and extent of the combustion zone 84. It willbe seen to begin slightly forward ofthe plane of the flange 76 withinthe combustion cone andto extend external of this cone and downstreamtherefrom.

The nozzle block is preferably made from east 11011 while the combustioncone must be of a metal which is capable of withstanding the thermalstresses set up within it by virtue of its configuration and thetemperature gradients existing in the cone. material for the combustioncone is Hastelloy X having 7 a thickness of 0.040 inch.

Theremaining portion of the. central block is made up of solidsections70.- Finally as illustrated in FIG. '1 the forward plate 62 hasanopening72 in. which is mounted a protective sleeve 73 extending internallyoftheihousing.

The sleeve 73 serves as a means for supporting and pro-' tecting thelight pipe 40. Between the internal wall *of the sleeve 73 and thesurface of light pipe .40 is an annular passage 74 through which-airflows as indicated by the arrows. Thus the light pipe is air-cooled andcontinuously cleaned by air passing over it. It will also I be seen thatin this arrangement the-light'responsive means, typically a cadmiumsulfide photocell, associated with the light pipe is protected from heatwhich would It will be seen from FIGSpl and 2 that there are in 'fact iin the nozzle system of this invention two distinctfluid flow paths, onewhich is axial, the other tangential; The result of thiscombinationof'flow paths is to produce a vortex around the transduceratomizing surface tip. This means that the atomizing surface 13 as wellas a portion of the small diameter section 12 of the horn is surroundedby swirling air resulting from the axially introduced air mixing withthetangentially directed This combination of flow paths is. importantsince the free. vortex" around the horn tip causes. strong recirculationcurrents downstream of the tip thus. promoting rapid, clean combustion.Then the tangentially directed air picks. up the fuel oil droplets,which because of their lack of kinetic energy would normally dropdownwardly, and maintains them in the combustion air. The combustioncone. in turn confines the vortex so that its energy cannot bedissipated before vaporization is complete. It is, of course,

the function of the combustioncone to insure clean com-' bustion andmaintain the droplets suspended in the. air until they are essentiallycompletely vaporized and at least partially burned. a 7

\Each of the two air passages-has associated with it .a cross-sectionalarea; and the sizing of these air passages is important since [thesmaller the total cross-sectional.

flow area, the greater the pressure required; Not only is it desirableto be able to adjust flow area and pressure, a

but it is also desirable to maintain the pressure requirement at arelatively low level to .make possible. theme of inexpensiveblowersystems; However, excessivenoz 1 zle areas, withattendant lowpressures,lead to poor. com.-

bustion efficiency because of low air velocity and low turbulence. It istherefore preferable 'thatnozzlei'pressures. be maintained between 0.50and 0.75 inchcf water column.

Another parameter ofthe" nozzle system of thisinvem tion is the ratio oftangential nozzle area (i.e.,"theftota=l cross-sectional area of thetangential passages 69 of 'FIG."

2) to the cross-sectional area of the axial passage (the annular channeldefined between the end plate 65 and the smaller diameter section 12 ofthe stepped hcrn).' If the 1 axial flow is very large compared to thetangential flow,

As an example one suitable the flame will tend to blow off. If on theother hand the tangential flow is excessively large compared to theaxial flow, the high swirl velocity created by the air enteringtangentially through passages 69 will centrifuge the oil droplets fromthe air and cause them to impinge on the internal walls of thecombustion cone 75, and then to collect in the cone. I

Generally the ratio of cross-sectional area of the tangential passagesto the cross-sectional area of the axial passage will range betweenabout 2.5 and 3.5. As an example, a burner designed to consume aboutone-half gallon of fuel oil per hour has been found to have an optimumratio at 13.3; while for a burner designed to consume about one-quartergallon per hour the ratio is preferably 2.8. Under these circumstancesthe minimum acceptable nozzle pressure for the first consumption rate isabout 0.7 inch water column; while for the lower consumption rate theminimum nozzle pressure is about 0. 5 inch water column.

It will of course be understood that for each burner design and fuel oilconsumption rate the ratio of the cross-sectional area of the two typesof air passages will vary and can be readily determined experimentally.This is also true in determining an optimum nozzle pressure. In general,the cross-sectional areas of the tangential passages and of the axialpassage must be balanced to maintain a stable flame within thecombustion zone and to support the fuel droplets until burned within thecombustion zone without causing any appreciable quantity to impinge onthe Wall of the combustion cone.

:In the operation of the fuel oil burner illustrated in FIG. 1 as anexample, metered fuel oil is provided at the atomizing surface 13 whichis oscillated at an ultrasonic frequency by means of the transducerwhich includes the two crystals and the electrode with its attendantpower and feedback circuit generally indicated at 26. in

operation a solenoid control switch attached to a thermostat, inaccordance with known practice, actuates the power feed to theelectrodes 46 and 48 when ignition is desired. Subsequent to theignition of the fuel oil and air the power to the electrodes is cut offby virtue of the actuation of the control mechanism 43 which receives asignal from photocell 41 which in turn is actuated by light transmittedthereto through light pipe 40. The light pipe 40 is so positioned thatit is able to see refiected light from the combustion zone. With theestablishment of a stable combustion zone ignition is no longerrequired.

Air entering the interior 52 of the burner housing is swept along pastthe transducer mechanism keeping it cool, and enters the combustion zonethrough the two paths described. The combustion air by the time itreaches the actual combustion zone has swept over the transducer, orother atomizing means, and the electrodes. In doing so it has maintainedthese elements at a relatively cool and constant temperature. Inaddition the location of the electrodes Within the tangential airpassages 69 permits a continuous flow of air over the length of theelectrodes and thus provides for their continuous cleaning. This in turnreduces maintenance of the electrodes and of their attendant mechanismsto a minimum and insures reliable performance at all times.

The flow of air and fuel oil droplets entrained therein is such as toestablish a combustion zone essentially as shown in FIG. 3. Radiationfrom this combustion zone tends to heat the combustion air and partiallyvaporize the fuel prior to its entrance into the combustion zone.Vaporization is completed within the combustion zone.

Extensive experimental experience with the system has shown that aburner using an ultrasonic atomizer with the nozzle system of thisinvention is practical, even for small, :low flow rate fuel oil burners.Combustion efficiency is high as evidenced by flue gas analyses whichshowed 12 to 13% CO at 0-1 smoke. Finally, no measurable quantity ofunburned fuel oil has been collected in the combustion cone,illustrating the effectiveness of the nozzle system in maintaining thefuel oil droplets in the combustion air until vaporization andcombustion is accomplished.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efliciently attained and,since certain changes may be made in the above construction Withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween. I

I claim:

1. A burner adapted to burn atomized fuel oil in the form oflow-velocity particles in a continuously supplied stream of anoxygen-containing combustion fluid, comprising in combination (a)delivery means for providing at an atomizing surface low-velocity fueloil droplets which lack significant kinetic energy;

(b) means forming a central passage in which said delivery means islocated;

(c) means for axially directing a first portion of an oxygen-containingcombustion fluid around said delivery means into said central passage;

((1) means for tangentially directing a second portion of saidcombustion fluid into said central passage for mixing with said firstportion to form a fluid vortex around said fuel oil particles at thepoint of their delivery, said vortex being capable of suspending saidfuel oil particles; and

(e) int-perforate cone means, having an inwardly extending lipped edgeat its larger discharge end, in fluid communication with said centralpassage and defining a portion of a combustion zone whereby the fuel oilis substantially all vaporized and partially burned prior to itsdischarge from said cone means.

2. A burner in accordance with claim 1 wherein said means fortangentially directing said second portion of combustion fluid into saidcentral passage comprises multiple tangential fluid passages into saidcentral passage.

3. A burner in accordance with claim 1 further characterized by havingignition electrodes extending through said means for tangentiallydirecting said second portion of said fluid, the tips of said electrodesbeing positioned just upstream from the plane of said atomizing surfacelocated in said central passage whereby said electrodes are continuouslycooled and maintained essentially free from the accumulation of fuel oilthereon.

4. A burner in accordance with claim 1 wherein said means for providingsaid fuel oil droplets comprises a lowpressure spray nozzle.

5. A burner in accordance with claim 1 wherein said means for providingsaid fuel oil droplets comprises an ultrasonic atomizer, the atomizingsurface of which extends into said atomizing zone.

6. A burner adapted to burn atomized fuel oil in the form oflow-velocity particles in a continuously supplied stream of air,comprising in combination (a) means for atomizing said fuel oil toprovide it in the form of low-velocity particles;

(b) housing means surrounding said atomizing means;

(c) means for delivering combustion air under pressure into said housingmeans;

(d) a nozzle system adapted to mix the atomized fuel oil and air and todefine at least a portion of a combustion zone wherein substantially allof the atomized fuel is vaporized and partially burned, said nozzlesystem comprising in combination (1) a nozzle block which defines theforward end of said housing,

(2) means forming ,a central zone within said nozzle block into whichsaid fuel particles are delivered,

(3) means for axially directing a first portion of said combustion airaround said atomizing means said central zone, p

(4) means forming tangential passages within said nozzle block andadapted to tangentially, direct a second portion of said combustion airinto said central zone whereby said first and second portions of saidcombustion air mix to'form a vortex capable of suspending said fuel oilparticles,

(5) imperforate cone means, having an'inw'ardly extending lipped' edgeat its larger dischargeend, in fluid communication with said centralzone and defining a portion of a combustion zone whereby the fuel oil issubstantially all vaporized' and partially burned prior to its dischargefrom said cone means; and a (e) electrode ignition means extending intosaid cen- "tral zone through said tangential passages and positionedjust upstream from the point of delivery of said atomized fuel.

7. A burner in accordance with claim 6 wherein said atomizing means isan ultrasonic atomizer, the atomizing surface of which extends into saidcentral zone.

8. A burner in accordance with claim 7 further characterized .in thatsaid means for axiallydirecting said combustion air into said centralzone comprises an annular passage surrounding the portion of saidultrasonic atomizer extending into said central zone.

9. A burner in accordance with claim 6further characterized by having(a) light pipe means, formed of a light transmitting heat-resistantmaterial, located to absorb and transmit radiation from said combustionzone and positioned within a sleeve extending into said housing wherebya small portion ofsaid combustion air in passing through said sleevecools said light pipe means; and

(b) light responsive means associated with said light pipe means andadapted to effect control of said electrode ignition means by respondingto radiation from said combustion zone transmitted by said light pipe.

10. Burner in accordance .with claim 6 further characterized in thatsaid cone means is afiixed to said forward end of said housing through aflange coextensive with said forward end.

11. A burner inaccordance with claim 6 further characterized by havingan insulating gasket disposed between} said flange and said forward endof saidthousingr 12. A burner in accordancewith claim 6 wherein saidcone means terminates at its downstream end in a rounded configuration.a I 5 7 13. A burner in accordance with claim 6 wherein the ratio of thecross-sectional area of said tangential air passages to thecross-sectional area of'said axial passage ranges between about "2.5 and3.5, said cross-sectional areas being taken normal to the axis' of saidatomizing means and at the entrance to said central zone.

References Cited by the Examiner JAMES WESTHAVER, Primary Examiner.

Dedication 3,275,059.J0lm E. McCullough, Carlisle, Mass. NOZZLE SYSTEMAND FUEL OIL BURNER INCORPORATING IT. Patent; dated Sept. 27, 1966.Dedication filed Oct. 20, 1969, by the assignee, American PetroleumInstitute. Hereby dedicates to the Public the entire remaining term ofsaid patent.

[Oflicial Gazette January 20, 1.970.]

1. A BURNER ADAPTED TO BURN ATOMIZED FUEL OIL IN THE FORM OFLOW-VELOCITY PARTICLES IN A CONTINUOUSLY SUPPLIED STREAM OF ANOXYGEN-CONTAINING COMBUSTION FLUID, COMPRISING IN COMBINATION (A)DELIVERY MEANS FOR PROVIDING AT AN ATOMIZING SURFACE LOW-VELOCITY FUELOIL DROPLETS WHICH LACK SIGNIFICANT KINETIC ENERGY; (B) MEANS FORMING ACENTRAL PASSAGE IN WHICH SAID DELIVERY MEANS IS LOCATED; (C) MEANS FORAXIALLY DIRECTING A FIRST PORTION OF AN OXYGEN-CONTAINING COMBUSTIONFLUID AROUND SAID DELIVERY MEANS INTO SAID CENTRAL PASSAGE; (D) MEANSFOR TANGENTIALLY DIRECTING A SECOND PORTION OF SAID COMBUSTION FLUIDINTO SAID CENTRAL PASSAGE FOR MIXING WITH SAID FIRST PORTION TO FORM AFLUID VORTEX AROUND SAID FUEL OIL PARTICLES AT THE POINT OF THEIRDELIVERY, SAID VORTEX BEING CAPABLE OF SUSPENDING SAID FUEL OILPARTICLES; AND (E) IMPERFORATE CONE MEANS, HAVING AN IMWARDLY EXTENDINGLIPPED EDGE AT ITS LARGER DISCHARGE END, IN FLUID COMMUNICATION WITHSAID CENTRAL PASSAGE AND DEFINING A PORTION OF A COMBUSTION ZONE WHEREBYTHE FUEL OIL IS SUBSTANTIALLY ALL VAPORIZED AND PARTIALLY BURNED PRIORTO ITS DISCHARGE FROM SAID CONE MEANS.